(1) Field of the Invention
The present invention relates to a rotary wing aircraft that has a hybrid power plant.
The present invention thus relates to the field of aircraft that include in particular a rotary wing. More particularly, the invention relates to aircraft having a so-called “hybrid” power plant for driving rotation of at least one rotor of a rotary wing via a main gearbox of the aircraft. Such a main gearbox is referred to more simply by its initials “main gearbox”.
(2) Description of Related Art
A “hybrid” power plant designates an installation having at least one fuel-burning engine and at least one electrical member, each of them being suitable for driving the main gearbox.
The electrical member may be an electric motor, i.e. an electrical appliance that performs a driving function only.
Nevertheless, the electrical member may also be an electrical machine, i.e. an electrical appliance that performs both a driving function and an electricity generator function. An electrical machine can thus operate in an electric motor mode for driving rotation of mechanical members, or else in an electricity generator mode for generating electrical energy. An electrical machine is sometimes said to be “reversible” insofar as the electrical machine can switch from an electric motor mode to the electricity generator mode, and vice versa.
It should be observed that an electricity generator is an electrical appliance that performs solely a function of generating electricity.
A rotary wing aircraft may have one or more lift-providing rotors referred to as “main” rotors, and possibly one or more auxiliary rotors, e.g. for controlling the yaw movement of the aircraft.
The power plant then has at least one engine for driving the main rotors via the main gearbox.
The engine co-operates with a first electrical machine. This first electrical machine operates in electric motor mode when starting the aircraft in order to start the engine.
For example, the engine may be a turbine engine having a gas generator. The first electrical machine then serves to drive the gas generator in rotation on starting.
Once the engine has started, the first electrical machine can then operate in electricity generator mode in order to feed electrical energy to the on-board network of the aircraft.
The first electrical machine then transforms electrical energy into mechanical energy in order to start the engine as a first function, and transforms mechanical energy coming from the engine into electrical energy for the on-board network as a second function.
Furthermore, a hybrid power plant may include an auxiliary energy delivery system for adding to or replacing the drive produced by an engine by means of an electrical power plant mechanically connected to a main gearbox.
According to document FR 2 962 404, a second electrical machine is thus connected to the main gearbox.
The second electrical machine then transforms electrical energy into mechanical energy in order to drive the main gearbox as a third function, and transforms mechanical energy coming from the main gearbox into electrical energy for the on-board network as a fourth function.
Document FR 2 962 404 thus describes an electrical machine that is mechanically connected to an engine, and an electrical machine that is mechanically connected to a main gearbox.
That type of configuration is advantageous, but it can be relatively heavy and bulky by ensuring redundancy for the electrical machines.
In addition, the first electrical machine is capable of taking mechanical energy from the gas generator of the engine. The engine then runs the risk of operating at a compression ratio that is not optimized, thereby leading to a drop in its specific fuel consumption.
In conclusion, it can be understood that it is not easy to design, adapt, and implement a hybrid power plant and its configuration.
Document FR 2 929 324 describes a turbine engine connected to an electrical machine.
Document WO 2012/059671 describes a method of optimizing the specific fuel consumption of a twin-engine helicopter and a twin-engine configuration with a regulator system for operating it.
Also known are documents US 2011/304156 and EP 2 148 066.